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29 Mar 1993

Volume 62, Issue 13, pp. 1445-1570

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Fabrication of a novel electro‐optical intensity modulator from the conjugated polymer, poly(2,5‐dimethoxy‐p‐phenylene vinylene)

I. D. Parker, R. W. Gymer, M. G. Harrison, R. H. Friend, and H. Ahmed

Appl. Phys. Lett. 62, 1519 (1993); http://dx.doi.org/10.1063/1.108626 (3 pages) | Cited 15 times

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We report an electro‐optic absorption modulator based around a metal‐insulator‐semiconductor field‐effect transistor structure in which the active semiconductor is the polymer poly(2,5‐dimethoxy‐p‐phenylene vinylene). It incorporates a single optical waveguide formed by the polymer, insulator, and a polyimide top layer which is ribbed to define the guide laterally. Charge injection creates polaron and bipolaron states which change the subgap absorption between 2 and 1.4 μm and between 800 nm and the band edge at 600 nm.
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42.79.Hp Optical processors, correlators, and modulators
78.20.Jq Electro-optical effects

Cyclotron resonance studies of two‐dimensional holes in strained Si1−xGex/Si quantum wells

J.‐P. Cheng, V. P. Kesan, D. A. Grutzmacher, T. O. Sedgwick, and J. A. Ott

Appl. Phys. Lett. 62, 1522 (1993); http://dx.doi.org/10.1063/1.108627 (3 pages) | Cited 19 times

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Far‐infrared magnetotransmission spectroscopy has been employed to study p‐type modulation‐doped strained Si1−xGex/Si quantum wells grown by atmospheric pressure chemical vapor deposition at magnetic fields up to 23 T. The cyclotron resonance (CR) mass of the two‐dimensional hole gas (2DHG) in a strained 7.5 nm Si0.63Ge0.37 quantum well was determined to be (0.29±0.02)m0 for a 2D hole density of 2.3×1012/cm2 at 3 K. The CR mass of 2DHGs in strained Si1−xGex is comparable to previous measurements of the CR mass of 2DHGs in strained InyGa1−yAs with similar 2D hole densities.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Effect of oxygen concentration on the kinetics of thermal donor formation in silicon at temperatures between 350 and 500 °C

C. A. Londos, M. J. Binns, A. R. Brown, S. A. McQuaid, and R. C. Newman

Appl. Phys. Lett. 62, 1525 (1993); http://dx.doi.org/10.1063/1.108628 (2 pages) | Cited 19 times

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Early measurements of the initial rate of thermal donor formation in Czochralski silicon at 450 °C revealed a dependency on the fourth power of the oxygen concentration. This result has led to the view that the core of the defects contained four oxygen atoms. We now show that this dependency is observed only for anneals close to 450 °C. Our results indicate that oxygen dimerization controls the thermal donor formation kinetics but that the dimers become increasingly unstable above 400 °C.
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61.72.Cc Kinetics of defect formation and annealing
71.55.Cn Elemental semiconductors

Conditions for the formation of defect‐induced bound exciton emissions in GaAs grown by molecular beam epitaxy

Nobukazu Ohnishi, Yunosuke Makita, Hisao Asakura, Tsutomu Iida, Akimasa Yamada, Hajime Shibata, Shin‐ichiro Uekusa, and Tokue Matsumori

Appl. Phys. Lett. 62, 1527 (1993); http://dx.doi.org/10.1063/1.108629 (3 pages) | Cited 9 times

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Conditions for the formation of defect‐induced bound exciton (DIBE) emissions in GaAs were investigated by molecular beam epitaxial method. Growth was made on both A‐ and B‐polarity substrates with (321), (221), and (211) orientations. For A‐polarity samples, (321)A and (211)A presented pronounced DIBE emissions. (221)A, however, exhibited no DIBE emission, instead it presented a dominant carbon donor‐carbon acceptor pair emission together with a small hump due to carbon donor‐related bound exciton emissions. For B‐polarity specimens, DIBE was completely vanished in all the three samples. It was theoretically demonstrated that DIBE is formed only when double‐handed Ga adatom site is existing.  
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Memory effects of silicon‐implanted oxides for electrically erasable programmable read‐only memory applications

Ming‐yin Hao, Hyunsang Hwang, and Jack C. Lee

Appl. Phys. Lett. 62, 1530 (1993); http://dx.doi.org/10.1063/1.108630 (3 pages) | Cited 17 times

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The memory effects of silicon‐implanted oxides are reported in this letter. Due to the trap‐like characteristics of the implanted silicon, hysteresis capacitance‐voltage loops have been measured after voltage pulse stressing. A positive voltage pulse leads to a positive shift of the capacitance‐voltage curve, while a negative voltage stress results in a negative drift. It was found that using these Si‐implanted oxides, writing/erasing operations of electrically erasable programmable read‐only memories could be realized by applying short voltage pulses (e.g., 100 ns, ±12–16 V). Moreover, excellent retention characteristics were also detected for these memory devices. The implanted silicon alters the conduction mechanism such that the I‐V behavior does not follow the Fowler–Nordheim tunneling. The implantation process did not yield noticeable degradation to the oxide quality; and a lifetime over 10 yr can be achieved even with ±16 V stressing.
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85.30.Tv Field effect devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Wannier–Stark quantization by internal field in the HgTe/CdTe superlattice

Ikai Lo, W. C. Mitchel, K. A. Harris, R. W. Yanka, L. M. Mohnkern, A. R. Reisinger, and T. H. Myers

Appl. Phys. Lett. 62, 1533 (1993); http://dx.doi.org/10.1063/1.108631 (3 pages) | Cited 5 times

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The Stark ladder can be formed in a semiconductor superlattice by an applied electric field. The localization of electrons by an external electric field is known as Wannier–Stark quantization. We have performed the Shubnikov–de Haas measurements with a tilted magnetic field and the photoluminescence measurement on a HgTe/CdTe superlattice in the absence of an external electric field. From the observation of a two‐dimensional electron gas and a blueshift of the photoluminescence spectrum, we conclude that the Stark ladder exists in the HgTe/CdTe superlattice and it is formed due to the Wannier–Stark quantization by the internal electrostatic field.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.55.Et II-VI semiconductors

Structure and location of misfit dislocations in InGaAs epilayers grown on vicinal GaAs(001) substrates

Y. Chen, N. D. Zakharov, P. Werner, Z. Liliental‐Weber, J. Washburn, J. F. Klem, and J. Y. Tsao

Appl. Phys. Lett. 62, 1536 (1993); http://dx.doi.org/10.1063/1.108632 (3 pages) | Cited 11 times

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The atomic structure of misfit dislocations at In0.2Ga0.8As/GaAs interfaces misoriented 2°–10° from (001) has been investigated by high‐resolution electron microscopy. The misfit dislocations are predominantly dissociated 60° dislocations consisting of 90° and 30° Shockley partial dislocations and enclosed stacking faults. These dissociated 60° dislocations form increasingly asymmetrically on the different {111} glide planes as the misorientation increases. The 90° partial dislocations are not confined to the interface, but lie 0–100 Å beneath it. The 30° partial dislocations, in turn, are pushed even further into the substrate.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Model for dielectric growth on silicon in a nitrous oxide environment

Sima Dimitrijev, Denis Sweatman, and H. Barry Harrison

Appl. Phys. Lett. 62, 1539 (1993); http://dx.doi.org/10.1063/1.108633 (2 pages) | Cited 23 times

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In this letter, a model for growth kinetics of ultrathin dielectrics obtained by oxidation of silicon in a nitrous oxide environment is proposed. The model assumes that the oxide growth is limited by time‐dependent interface reaction, which is slowed down and eventually completely blocked as oxide growth sites are neutralized by nitrogen atoms. The model fits experimental data extremely well, both with time and temperature.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films
81.65.-b Surface treatments
85.40.Bh Computer-aided design of microcircuits; layout and modeling

Anomalous diffusion of nitrogen in SiO2 under ion bombardment

Indrajit Banerjee and Dimitry Kuzminov

Appl. Phys. Lett. 62, 1541 (1993); http://dx.doi.org/10.1063/1.108634 (3 pages) | Cited 15 times

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Depth profiling was done by secondary ion mass spectrometry (SIMS) on SiO2/Si3N4/SiO2 (ONO) structures to determine if the nitrogen tail seen going into the silicon substrate was real or an artifact of ion bombardment. To determine this without an element of doubt, samples were thinned from the back side to the ONO layer and SIMS depth profiling was carried out on the exposed underside of ONO. It is determined that the layer of ‘‘nitride’’ at the Si/oxide interface is really an artifact of ion bombardment. Profiling from the back side shows there is no nitrogen tail in the silicon substrate and there is also no nitride at the oxide/Si interface. The interfacial nitride layer, and the apparent nitrogen tail extending into the underlying Si, seen from front‐side profiling, are due to anomalous nitrogen diffusion during ion bombardment. It is believed that nitrogen‐oxygen complexes are formed in the silicon substrate as a result of nitridation, and this adversely affects device performance. Though this may still be true, one needs to be cautious in interpreting SIMS and Auger depth profiles from the front side in order to corroborate the electrical results.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
66.30.J- Diffusion of impurities
61.80.Jh Ion radiation effects

Investigations of quantum trench tunneling diodes

A. J. Peck, S. J. Bending, K. von Klitzing, and K. Ploog

Appl. Phys. Lett. 62, 1544 (1993); http://dx.doi.org/10.1063/1.108635 (3 pages) | Cited 3 times

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We report on the realization of a new type of lateral tunneling diode with the potential for ultrahigh frequency (THz) operation. The diodes, which are fabricated by etching tiny quantum trenches into the surface of a GaAs/AlGaAs heterostructure, display extremely nonlinear current‐voltage characteristics. Tunneling barrier heights are obtained from a study of thermally activated current, and results are compared to those of a theoretical model of the structure based on the finite difference form of the Poisson equation.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

In situ approach to realization of three‐dimensionally confined structures via substrate encoded size reducing epitaxy on nonplanar patterned substrates

A. Madhukar, K. C. Rajkumar, and P. Chen

Appl. Phys. Lett. 62, 1547 (1993); http://dx.doi.org/10.1063/1.108636 (3 pages) | Cited 21 times

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We report the first realization of three‐dimensionally confined semiconductor heterostructures via a one‐step growth on nonplanar patterned substrate. Truncated pyramidal shaped mesas on GaAs (111)B patterned substrates are employed and a substrate encoded size reducing epitaxical growth process exploited to realize GaAs pinched‐off pyramidal volumes of base ∼50 nm and height 13 nm.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.-a Thin film structure and morphology

All‐optical, high contrast GaAlInAs multiple quantum well asymmetric reflection modulator at 1.3 μm

M. F. Krol, T. Ohtsuki, G. Khitrova, R. K. Boncek, B. P. McGinnis, H. M. Gibbs, and N. Peyghambarian

Appl. Phys. Lett. 62, 1550 (1993); http://dx.doi.org/10.1063/1.108637 (3 pages) | Cited 11 times

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A high contrast, low intensity GaAlInAs/AlInAs multiple quantum well asymmetric Fabry–Perot reflection modulator for operation at 1.3 μm has been demonstrated. The reflection modulator takes advantage of the large absorptive and refractive nonlinearities associated with saturating the heavy‐hole exciton resonance. We achieve an on/off contrast ratio in excess of 1000:1 (30 dB) and an insertion loss of 2.2 dB at a pump intensity of 30 kW/cm2, corresponding to a carrier density of 4.5×1017 cm−3. The modulator was demonstrated to have a large operating bandwidth, achieving an on/off contrast ratio of greater than 100:1 over a 5 nm optical band. The operating speed of the modulator was measured and found to approach 1 GHz.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.66.Fd III-V semiconductors

Evidence for preferential formation of the (Bi,Pb)2Sr2Ca2Cu3Ox phase at the Ag interface in Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3Ox tapes

Yi Feng, Y. E. High, D. C. Larbalestier, Y. S. Sung, and E. E. Hellstrom

Appl. Phys. Lett. 62, 1553 (1993); http://dx.doi.org/10.1063/1.108638 (3 pages) | Cited 48 times

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Studies of the phase evolution in Ag‐sheathed (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes processed with fine aerosol spray pyrolysis powder show that the 2223 phase always forms preferentially at the Ag interface at temperatures lower than those needed to form 2223 away from the Ag. The 2223 basal planes align themselves with the Ag surface and 2223 can penetrate into the Ag where the interface undulates. In the interior of the Bi‐Sr‐Ca‐Cu‐O core, away from the Ag, reaction to alkaline earth cuprate is favored over reaction to 2223. These results provide direct evidence of the beneficial role that Ag plays in developing the 2223 phase and emphasize the need to produce smooth Ag interfaces to attain highly aligned 2223.
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84.71.Mn Superconducting wires, fibers, and tapes
74.72.-h Cuprate superconductors
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Isotropic Jc‐B properties of YBa2Cu3O7−x thin films containing fine precipitates by metalorganic chemical vapor deposition

S. Matsuno, S. Kinouchi, K. Egawa, T. Umemura, F. Uchikawa, and S. Nakabayashi

Appl. Phys. Lett. 62, 1556 (1993); http://dx.doi.org/10.1063/1.108639 (3 pages) | Cited 1 time

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Y1Ba2Cu3O7−x superconducting thin films which have isotropic Jc‐B properties were prepared onto SrTiO3 (100) substrates at 700 °C by metalorganic chemical vapor deposition. The Jc did not depend on directions of the field either perpendicular or parallel to the c axis of the films and the films had a high Jc of 6.1×104 and 7.1×104 A/cm2 at 77 K and 5 T perpendicular and parallel to the c axis, respectively. Transmission electron microscopy observation and x‐ray energy dispersive spectroscopy analysis indicated that the films contained many fine Y2BaCuO5‐like precipitates with diameter of ∼10 nm and they were distributed uniformly with the density Np as high as 1023/m3.
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74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors

Highly stabilized sputter deposition of YBa2Cu3O7

U. Krüger, R. Kutzner, R. Wördenweber, G. Mank, and A. Kraemer‐Flecken

Appl. Phys. Lett. 62, 1559 (1993); http://dx.doi.org/10.1063/1.108640 (3 pages) | Cited 6 times

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A method of stabilizing and homogenizing the plasma during on‐axis high‐pressure dc sputter deposition of YBa2Cu3O7 is introduced, which leads to improved reproducibility and uniformity of the deposition process. The plasma is monitored and controlled via optical emission spectroscopy. Strong changes of the plasma intensity and intensity profile above the target are observed in the standard sputter process, which lead to unstable and inhomogeneous deposition of high Tc material. These changes are counteracted by adequate variation of the composition of the process gas (Ar/O2). The intensity of the plasma flicker is thus reduced by a factor of 4–5, long term drifts in the plasma intensity, and arcing of the plasma are eliminated.  
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81.15.Cd Deposition by sputtering
74.72.-h Cuprate superconductors

Annealing effects on multilayered Co/Pt and Co/Pd sputtering films

H. Yamane, Y. Maeno, and M. Kobayashi

Appl. Phys. Lett. 62, 1562 (1993); http://dx.doi.org/10.1063/1.108641 (3 pages) | Cited 9 times

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Effects of air annealing on magnetic properties and structures of multilayered Co/Pt and Co/Pd sputtering films were studied. The dual‐source rf magnetron sputtering method was employed in fabricating the films. The thicknesses of the Co layer and Pt layer of the Co/Pt films were 4.3 and 10.0 Å, respectively: the total thickness was 4300 Å. The thicknesses of Co layer and Pd layer of the Co/Pd films were 3.6 and 11.8 Å, respectively: the total thickness was 5600 Å. Residual magnetizations and coercivities of the Co/Pt and Co/Pd films increased with air‐annealing at 250–350 °C for 30 min to 2.5–3 kG and 2–3 kOe, respectively. The increases were observed only during air annealing, but not in vacuum annealing. Saturated magnetizations and intensities of the superlattice x‐ray peak decreased uniformly relative to annealing temperature.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Epitaxial growth of ferromagnetic ultrathin MnGa films with perpendicular magnetization on GaAs

M. Tanaka, J. P. Harbison, J. DeBoeck, T. Sands, B. Philips, T. L. Cheeks, and V. G. Keramidas

Appl. Phys. Lett. 62, 1565 (1993); http://dx.doi.org/10.1063/1.108642 (3 pages) | Cited 86 times

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We have successfully grown ferromagnetic MnGa ultrathin films on GaAs substrates by molecular beam epitaxy. Reflection high energy electron diffraction and cross‐sectional transmission electron microscopy show that monocrystalline MnGa films are grown with the c axis of the tetragonal unit cell normal to the (001) GaAs substrates. Both magnetization measurements by vibrating sample magnetometer and extraordinary Hall effect (EHE) measurements indicate perpendicular magnetization, with the remnant magnetization of 225 emu/cm3 and EHE resistivity in the range of 0.5–4 μΩ cm at room temperature. The material possesses properties ideal for certain nonvolatile magnetic memory coupled with underlying III‐V circuitry.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.70.-i Magnetic properties of thin films, surfaces, and interfaces
75.30.Gw Magnetic anisotropy

Raman spectroscopy and the effects of ultraviolet irradiation on polyimide film

X. J. Gu

Appl. Phys. Lett. 62, 1568 (1993); http://dx.doi.org/10.1063/1.108643 (3 pages) | Cited 3 times

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Raman spectra of polyimide films were studied before and after being irradiated with 308 nm excimer laser pulses in order to understand the conductivity increase induced by ultraviolet irradiation. Changes in the chemical structure of polyimide were observed. A possible mechanism responsible for the ultraviolet induced conductivity increase is proposed. This letter also shows that the Raman microprobe can be very useful in the analysis of the molecular structure of polymers.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
73.61.Ph Polymers; organic compounds
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
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